The invention relates to carburation devices for internal combustion engines, of the type having an idling circuit opening into that part of the induction passage which is downstream of a throttle actuated by the operator, said idling circuit comprising an idling duct through which a primary fuel-air mixture is delivered to the induction passage downstream of the throttle, at least when the latter is in its minimum opening position leaving an air flow passage between the throttle and the induction passage wall, and a channel having an adjustable cross-sectional area for delivery of an additional quantity of air enriched with primary air-fuel mixture to flow from upstream to downstream of the throttle.
According to the invention, there is provided a carburation device comprising a solenoid valve having two positions, disposed in the path of at least a fraction of said additional fuel enriched air, and a solenoid valve control circuit comprising an engine speed probe and which in operation supplies the solenoid valve with electric pulses with a variable duty cycle so as to prevent the engine speed from falling substantially below a given idling speed and to give the solenoid valve a duty cycle in dependence on the engine speed above a preset value thereof, during deceleration of the engine fed by the carburator device.
Advantageously the solenoid valve is of the kind which takes up a fully open position when energized and a minimum non-zero closed position when de-energized.
The pulse supply circuit can be designed so that the preset idling speed can be slightly varied in dependence on an engine operating parameter, inter alia the temperature of a cooling or lubricating fluid. It is known that, until the engine has reached its operating temperature, it should preferably be given an idling speed above the normal idling speed.
The solenoid valve energization circuit will normally detect deceleration as a result of the simultaneous presence of two input signals, one indicating that an accelerator pedal is at rest and the other that the engine speed exceeds a preset value. On a car the engine speed can be measured directly, or the output speed of the driving shaft can be measured, subject to the additional condition that the gearbox is at the higher ratio.
The invention will be better understood from the following description of a carburation device constituting an embodiment, given by way of example. The description refers to the accompanying drawings.